(i) Field of the Invention
The present invention relates to a vehicle to roadside communication by the use of a plurality of road side equipments and on-vehicle equipments carried on a plurality of vehicles.
(ii) Description of the Related Art
Heretofore, it has been suggested that communication equipments (road side equipments) are arranged on a road, and vehicle to roadside communication is carried out between the road side equipments and a communication equipment carried on a vehicle (an on-vehicle equipment) to perform interchange of information. For example, if a vehicle receives position information, the information of the present position of the vehicle can be revised in a navigation device or the like. Furthermore, if the vehicle receives accident information and congestion information from the road side equipments, these information items can be utilized to select a route and the like. Moreover, if the information of the destination of the vehicle is sent from the on-vehicle equipment to the road side equipment, the vehicle can obtain information about an optimum route to be selected. On the other hand, the road side equipments can ascertain the number of passed vehicles as a result of the communication with the vehicles, and if the road side equipments receive the information of the ID numbers or the like of the vehicles, a time required for the car to pass between the road side equipments can be recognized. In addition, if the road side equipments receive the destination information from the vehicles, the number of vehicles which will pass a certain district in the future can be predicted. Therefore, if many road side equipments are collectively supervised, the traffic situation in the district can be correctly ascertained, and thus a proper traffic restriction, the supervision of signals and the supply of optimum route information can be accomplished.
The above-mentioned vehicle to roadside communication system can be classified into a system by radio and a system using rays such as infrared rays. Radio is a system which has been widely used as a communication means, and it can be considered that radio is easily applicable to the vehicle to roadside communication. On the other hand, in the system using rays such as infrared rays, devices for sending and receiving signals are inexpensive, and since they have a high directivity, the system possesses a merit that interference can be prevented. For these reasons, the system using rays has also been investigated together with the system using radio, so as to put them to practical use. In this connection, the vehicle to roadside communication using rays has been disclosed in Japanese Utility Model Laid-open Publication No. Hei 4-24200.
In such a communication, the generation of errors is an unavoidable problem, and a measure against the errors is necessary. Particularly in the vehicle to roadside communication in which two-way communication is performed, it is difficult to specify whether a cause of the error resides in the road side equipment or the on-vehicle equipment. Therefore, the equipment causing the communication error cannot be specified, and so there is a problem that it is difficult to promptly carry out proper maintenance or error processing for such an equipment.